Personal care absorbent products, such as infant diapers, adult incontinent pads, and feminine care products, typically contain a fluid absorbent core. Many absorbent articles include the fluid absorbent core disposed between a top sheet and a back sheet. The top sheet is typically formed from a fluid-permeable material adapted to promote fluid transfer into the absorbent core, such as upon a liquid insult, usually with minimal fluid retention by the top sheet. U.S. southern pine fluff pulp is commonly used in the absorbent core, generally in the form of a fibrous matrix, and sometimes in conjunction with a superabsorbent polymer (SAP) dispersed throughout the fibrous matrix. This fluff pulp is recognized worldwide as the preferred fiber for absorbent products, based on factors such as the fluff pulp's high fiber length, fiber coarseness, and its relative ease of processing from a wet-laid and dried pulp sheet to an air-laid web. The raw material for this type of cellulosic fluff pulp is Southern Pine (e.g., Loblolly Pine, Pinus taeda L.,). The raw material is renewable, and the pulp is easily biodegradable. Compared to SAP, these fibers are inexpensive on a per mass basis but tend to be more expensive on per unit of liquid held basis. These fluff pulp fibers mostly absorb within the interstices between fibers. For this reason, a fibrous matrix readily releases acquired liquid on application of pressure. The tendency to release acquired liquid can result in significant skin wetness during use of an absorbent product that includes a core formed exclusively from cellulosic fibers. Such products also tend to leak the acquired liquid because liquid is not effectively retained in such a fibrous absorbent core.
SAPs are water-swellable, generally water-insoluble absorbent materials having a high absorbent capacity for fluids. They are used in absorbent articles like baby diapers or adult incontinent products to absorb and hold body fluids. SAP, upon absorption of fluids, swells and becomes a gel holding more than its weight of such fluids. The SAPs in common use are mostly derived from acrylic acid. Acrylic acid based polymers also comprise a meaningful portion of the cost structure of diapers and incontinent pads. SAPs are designed to have high gel strength (as demonstrated by high absorbency under load or AUL). The high gel strength (upon swelling) of currently used SAP particles helps them to retain significant void space between particles, which is helpful for rapid fluid uptake. However, this high “void volume” simultaneously results in significant interstitial (between particles) liquid in the product in the saturated state. When there is interstitial liquid the “rewet” value or “wet feeling” of an absorbent product is compromised.
Some absorbent articles, such as diapers or adult incontinence pads, also include an acquisition and distribution layer (ADL) for the collection and uniform and timely distribution of fluid from a fluid insult to the absorbent core. An ADL is usually placed between the top sheet and the absorbent core, and normally takes the form of composite fabric with most likely the top-one third of the fabric having low density (higher denier fiber) with relatively large voids and higher void volume for the effective acquisition of the presented fluid, even at relatively higher discharge rates. The middle one-third of the composite fabric of the ADL is usually made of higher density (low denier) fibers with smaller voids, while the lower one-third of the fabric is made of even higher density (lower and smaller denier) fibers and yet with finer voids. The higher density portions of the composite have more and finer capillaries and hence develop greater capillary pressure, thus moving greater volumes of fluid to the outer regions of the structure thus enabling the proper channelization and distribution of the fluid in an evenly fashion to allow the absorbent core to take up all of the liquid insult in a time bound manner to allow SAP within the absorbent core to hold and to gel the insult neither too slow nor too fast. The ADL provides for more rapid liquid acquisition (minimizing flooding in the target zone), and ensures more rapid transport and thorough distribution of the fluid into the absorbent core.
As noted above, the absorbent core is adapted to retain fluid, and as such may consist of one or more layers, such as layers to acquire, distribute, and/or store fluid. In many cases, a matrix of cellulose fibers, such as in the form of an air-laid pad and/or non-woven web, is used in (or as) the absorbent core of absorbent articles. In some cases, the different layers may consist of one or more different types of cellulose fibers, such as cross-linked cellulose fibers. The absorbent core may also include one or more fluid retention agents, such as one or more SAPs, distributed throughout the fiber matrix, usually as particles.
The back sheet is typically formed from a fluid-impermeable material to form a barrier to prevent retained fluid from escaping.
Whatever the structure, when the absorbent article is wet from one or more liquid insults, the chances for the fluid coming in contact with the skin increases profoundly, and if left unchanged for a long time can result in diaper rash for infants or dermatitis problem in adults, thereby posing a skin wellness hazard. However, in general, the only way to know whether the diaper or the incontinent pad is dry or wet is to physically inspect it. During day time this may not pose a significant problem because a caregiver can check the diapers or adult incontinent products as many times as desired. However, inspections during night time can be a discomfort to the baby as well as to the adult, disturbing their sleep. Moreover, frequent night time inspections, such as several times in a single night, can disrupt the wearer's sleeping pattern, which poses health hazard to baby as well as the adult patient.
In addition, it is typical that an article of clothing, such as pants, pajamas, and/or undergarments, is worn over the diaper or absorbent article. Accordingly, even absorbent articles that incorporate different types of wetness and/or moisture indicators pose difficulties in timely discovery of an insult.
As a result, there it typically a time lapse between the insult and its discovery. If this time period is prolonged then there exists the possibility of developing diaper rash, skin irritation, and/or skin flaking. These conditions can be very painful for those affected. This is particularly true for babies and those adults in care-giving facilities, and particularly true for night time insults, which can lead to longer periods prior to changing the absorbent article.
Previous moisture indicators incorporated into absorbent articles use color change as a visual indication of wetness detection. Inks that appear, or disappear, based on contact with liquid are popular mechanisms for wetness detection. Fluorescence has also been used for wetness detection, such as by incorporating a compound that fluoresces in the presence of a liquid. The mechanisms for such indicators generally fall into three broad categories: (1) imprinting a moisture indicating pattern on one of the piles of the absorbent article; (2) discrete moisture-indicating strips or layers that are incorporated between the layers of the absorbent article; and (3) a discrete (i.e., not part of the absorbent article's construction) indicating strip that is fastened to the interior of the absorbent article immediately prior to use.
Whatever the mechanism, these visual indicators are all deficient in low-light (e.g., night time) situations. Appearing or disappearing inks must be directly visually detected, such that the caregiver can see the absorbent product. In low-light situations, this may require both a light source (e.g., overhead light or flashlight), as well as the removal of covering garments (e.g., pajamas or undergarments). Fluorescent indicators suffer similar issues, in that they require an external light source to excite the fluorescent compound. Such excitation is typically provided by exposing the indicator to UV light (which presents health concerns to the wearer and caregiver) and must be in direct optical communication with the fluorescent compound, which then requires removal of covering garments, blankets, etc. Therefore, the use of visual indicators previously used to detect wetness in absorbent garments suffers many disadvantages in low-light situations, which greatly reduces the usefulness of their indication mechanisms.
Each of these solutions to wetness detection for absorbent articles is deficient for the needs of night insult detection. Chiefly, all technologies do not reliably trigger, and even when they do, require direct, lighted visual inspection to detect.
Therefore, present absorbent articles are inadequate when alerting a caregiver to insults occurring at night and/or under garments.